This project is concerned with the application of statistical methodology to laboratory animal experiments, with particular emphasis on long-term carcinogenicity studies. Specific areas that were the focus of research efforts during the past year included experimental design (e.g., selection of appropriate dose levels; use of dual control groups), data analysis (e.g., effect of tumor and treatment lethality on dose-related trends in tumor onset; developing new methodology that does not require cause of death information; assessing synergism in carcinogenicity studies), and interpretation of results (e.g., evaluating the effects of body weight, and time-related trends on tumor incidence; assessing inter-species correlation in neoplastic response). Other research efforts included assessing the relationship between toxicity/genotoxicity and chemically induced carcinogenesis in laboratory rodents, and investigating the possible influences of cage effects on liver tumor incidence for chemicals evaluated as hepatocarcinogens. Many of these investigations utilized the large data base of laboratory animal carcinogenicity studies carried out by the National Toxicology Program.